The number of updates was right on the average so far this year of seven per month, yet another indication that although Microsoft once used an even-odd schedule, patching more vulnerabilities in the even months, it has discarded the model.

This month's Patch Tuesday will fix the largest number of vulnerabilities -- 28 all told -- this year. In May, Microsoft fixed 23 security flaws.

Of the seven updates, Microsoft tagged three as "critical," the highest threat ranking in its four-step scoring, and the other four as "important," the next-most serious rating.

One update will address all supported versions of IE, ranging from the 11-year-old IE6 to last year's IE9; four will affect Windows; and the remaining pair will tackle vulnerabilities in all versions of Office on Windows and Dynamics AX 2012, an enterprise resource planning (ERP) product.

Storms singled out the IE update, identified in the advance notification as one of the three critical bulletins, as most likely to climb to the top of users' to-do lists.

"That's going to be the obvious one to deploy first," Storms said, using the long-established logic of security professionals to patch the browser with haste because of its widespread use and its broad attack surface.

Marcus Carey, a security researcher at Rapid7, agreed. "Browser exploits provide the most bang for the buck," Carey said in an email Thursday.

Storms suspected that the IE update will include a patch for one or more of the bugs used by a French security company to hack the browser at the 2012 version of Pwn2Own, an annual contest that pits researchers against software for cash prizes.

For its work, which included hacks of IE9 and Google's Chrome, Vupen took home $60,000 in prize money.

Last year, Microsoft patched the three IE bugs exploited in 2011's Pwn2Own with three separate bulletins shipped in April, June and August.

From Storm's perspective, this month is really Microsoft's first opportunity to patch any of the Vupen zero-days. "April was too soon," he argued, after the early-March contest. Microsoft's patch development, as well as the testing of those patches, usually takes more than 30 days.

The other stand-out of the seven updates slated for release next Tuesday is "Bulletin 3," said Storms, because it's marked critical and applies to all versions of Windows. "It's certainly on my list, because of its criticality and the fact that it applies to all [versions of] Windows up and down the stack," he said. "And depending on what it is, it maybe will even take the top spot."

Bulletin 1 could also be a dark horse, said Storms, who pointed out the unusual rankings Microsoft gave for some versions of Windows. For example, that update is rated "moderate" for Windows 7 RTM, or release to manufacturing -- the original 2009 version -- but critical for Windows 7 Service Pack 1 (SP1), which launched in February 2011.

The update is also rated critical for all versions of Windows Server, including 2003, 2008 and 2008 R2.

"It could be a change to Terminal Services," said Storms, referring to the service whose licensing certificate authority (CA) was exploited by hackers to generate fake Microsoft digital signatures, which were then used by Flame, a highly-advanced cyber-espionage tool.

Yesterday, Microsoft announced that it was updating Windows Update and WSUS (Windows Server Update Service) to revamp how it signs update files.

Storms said the update to Windows Update would delay the roll-out of next week's patches by enterprises that religiously test everything before deploying to their PCs and servers. "They'll want to test the Windows Update update," said Storms of businesses. "If that breaks, everything breaks with it."

If Microsoft provides the Windows Update and WSUS updates before Tuesday, companies will spend time testing that before allowing the month's patches to reach their systems.

A smarter move for Microsoft, said Storms, would be to push the Windows Update and WSUS changes after next Tuesday, even though that would run contrary to Microsoft's promise yesterday of starting to serve the changes this week.

Microsoft will release the seven updates at approximately 1 p.m. Eastern time on June 12.